1. Field of the Invention
The invention relates to a magnetic resonance (MR) method for determining a (MR) magnetic distribution in an examination area and for determining the position of at least one microcoil which is located in the examination area in or on an examination object, in which
a) a homogeneous stationary magnetic field acts on the examination area, PA1 b) at least one high-frequency (RF) pulse acting on the examination area is generated, PA1 c) after the high-frequency RF pulse an MR signal induced in the microcoil is detected under the influence of a gradient magnetic field that acts on the examination PA1 d) the position of the microcoil in the gradient direction defined by the gradient field is derived from the detected MR signal, PA1 e) the steps and b) to d) are repeated for another gradient direction, and PA1 f) MR signals are detected by a further receiving coil arrangement to determine the MR distribution, PA1 a) means for generating a homogeneous stationary magnetic field in an examination area, PA1 b) means for generating high-frequency pulses that act on the examination area, PA1 c) means for generating gradient magnetic fields that act on the examination area which fields have a controllable gradient direction, PA1 d) at least one microcoil for detecting MR signals, which is connected to a first receiver, PA1 e) a further receiver coil arrangement for detecting MR signals, which is connected to a second receiver, PA1 f) means for deriving the position of the microcoil from the MR signals detected by the first receiver, PA1 g) means for deriving the nuclear magnetic distribution from the MR signals detected by the second receiver, PA1 h) a control unit for controlling the further components of the MR device,
and relates to an arrangement for implementing this method.
A microcoil is denoted here and in the following as a coil that can only receive MR signals from an area that is small compared to the overall examination area. The gradient direction is denoted as the direction in which the gradient of the gradient magnetic field runs.
2. Description of the Related Art
An MR method of the type defined in the opening paragraph is known from U.S. Pat. No. 5,318,025. One or various microcoils is/are connected to an instrument, for example, a catheter, inserted into the body of a patient. The position of the microcoil is determined by three consecutive sequences which comprise a high-frequency pulse, after which an MR signal is received under the influence of a gradient magnetic field. The gradient directions for these three sequences correspond to the x, y and z direction. The spectrum of the MR signal, which corresponds to the Fourier transformation of the MR signal, has a maximum in the gradient direction in the examination area at the position from where the microcoil can detect an MR signal. In this manner the position of the microcoil can be monitored by determining the maxima in the three gradient directions.
Monitoring the position may be continued as long as this is desired. Alternatively, an additional receiver coil arrangement determines the MR data from which the MR distribution in the examination area i.e. an MR image, can be derived. The MR position data and the MR image data may also be determined in alternating fashion. The position data may then be superimposed on the generated MR image, so that a viewer can continuously determine and recognize the position of the instrument (catheter) in the MR image.
A disadvantage is that the image data and the position data are to be derived from MR signals which were detected at different instants. When the position of the microcoil in the MR image is represented, there may be errors when the anatomy of the patient changes, for example, by a movement, or by a surgical operation. Furthermore, there is the disadvantage that the sequences necessary for finding the position are to be generated in addition to the sequences necessary for the imaging, so that the patient is burdened even more.